1. Field of the Invention
The present invention relates to a scroll compressor, more particularly relates to a seal means suitable for providing a backpressure chamber supporting a thrust load of a scroll compressor.
2. Description of the Related Art
As described in Japanese Unexamined Patent Publication (Kokai) No. 2-176178, when driving a movable scroll to compress a fluid in a scroll compressor, a thrust load pressing the movable scroll to the fixed housing side is generated due to the compression reaction force. To support this thrust load, a ring-shaped thrust load support member comprised of a member comprised basically of for example cobalt or nickel and including a secondary ingredient such as molybdenum, chrome, silicon, or carbon or a wear resistant material comprised of carbon fiber bound by an epoxy resin is used between a back surface of an end plate of the movable scroll and the surface on the housing side facing this. With this configuration, however, heat of friction due to the sliding action is generated between the front surface of the thrust load support member and the surface of the opposing member and wear progresses, so in the related art, the measure has been devised of providing a groove in the ring-shaped thrust load support member to supply cooling water to absorb the heat of friction.
To suppress the heat of friction or wear in the thrust load support member generated in this way, as described in the invention previously proposed by the inventors and disclosed in Japanese Unexamined Patent Publication (Kokai) No. 9-310687, there is known a scroll compressor formed with a backpressure chamber as a recessed space in a back surface of an end plate of a movable scroll and guiding a compressed fluid from a discharge side to this backpressure chamber to cause the generation of a backpressure and thereby bias the movable scroll in an axial direction and reduce the large contact load acting between the back surface of the flat surface of the movable scroll on the housing side generated by the compression reaction force.
When working the related art described above, if the fluid to be compressed is one with a low working pressure as with the chlorofluorocarbons generally used as refrigerants in refrigeration cycles, the thrust load generated due to the compression force is around 1000N, so the pressure of the fluid introduced into the backpressure chamber of the back surface of the movable scroll may be low. Therefore, even if using a seal material for holding the pressure in the backpressure chamber, the load acting on the seal member will not become that large. Further, since the contact load is small, the lubrication state of the sliding surface of the seal member is believed to be in the fluid lubrication region, so an oil film is reliably formed on the surface of the housing side in sliding contact with the seal member and sliding contact is believed to be performed with a low coefficient of friction. Therefore, the mechanical loss due to the sliding action of the seal member can be kept low.
In a refrigeration cycle using as a refrigerant a so-called supercritical pressure fluid such as carbon dioxide (CO2), however, when compressing the refrigerant by a scroll compressor shown in the above related art, the thrust load acting on the movable scroll reaches as much as 7000N or about seven times the case of use of a refrigerant having a low working pressure such as a chlorofluorocarbon, so the pressure of the fluid introduced into the backpressure chamber similarly becomes a seven times higher pressure. This high-pressure acts on the seal member. Further, since the load acting on the seal member is high, the lubrication state of the sliding surface of the seal member is not in the fluid lubrication region, but is believed to be in the mixed lubrication region or boundary lubrication region where the coefficient of friction is high. Therefore, there is the problem that the mechanical loss due to the sliding action of the seal member becomes larger and causes a reduction in the efficiency of the compressor.
Therefore, in the related art later proposed by the inventors and disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2000-249086, there is described a scroll compressor using a supercritical pressure fluid as the refrigerant providing a seal member in a backpressure chamber of a movable scroll and taking out relatively low pressure refrigerant not yet compressed to a sufficiently high-pressure in the working chambers and supplying it to the backpressure chamber through a check valve so as to prevent in advance leakage of a large amount of high-pressure refrigerant from the backpressure chamber and so as to suppress an increase in the wear of the seal member or mechanical loss.
In this way, while the provision of a backpressure chamber behind an end plate of a movable scroll in order to support the thrust load in a scroll compressor and the provision of a seal member in the backpressure chamber in order to prevent leakage of the compressed fluid from the backpressure chamber are known even in a scroll compressor compressing a supercritical pressure fluid, details such as how to provide what kind of shape of seal member in the backpressure chamber have not yet been sufficiently researched.
Later research by the inventors proposing the above related art revealed that use of a seal member for the backpressure chamber having a joint such as in a piston ring of an internal combustion engine resulted in the problem of a large amount of high-pressure fluid supplied to the backpressure chamber leaking from the joint and that use of a continuous ring-shaped seal member not having any joint resulted in the problem of the compressed fluid entering the clearance between the seal member and wall surface of the backpressure chamber and therefore deformation of the seal member and obstruction of the action of closely contacting the wall surface of the backpressure chamber or the wall surface of the housing and a consequent inability to obtain a sufficient sealing effect.
An object of the present invention is to eliminate these problems in the related art by providing a seal means of a novel configuration in the backpressure chamber of a scroll compressor.
In order to deal with the above problems in the related art, the present invention provides a scroll compressor provided with a housing, a shaft having a crank part rotatably supported by the housing and partially offset, and a movable scroll having a spiral shaped blade and end plate and driven to orbit by the crank part of the shaft, and a fixed scroll having a spiral shaped blade meshing with the movable scroll and end plate and fixed to said housing, where when the movable scroll is driven to orbit by the crank part of the shaft, while a plurality of working chambers formed between the blade of the movable scroll and the blade of the fixed scroll move toward the center, the volumes of the working chambers are successively reduced and thereby the fluid is compressed in the working chambers, the scroll compressor further provided with: a middle housing provided as part of the housing behind the movable scroll for supporting a thrust load in an axial direction of the shaft acting on the movable scroll along with the rise in the compression pressure of the fluid in the working chambers; at least one ring-shaped groove forming a backpressure chamber in one of a back surface of the end plate of the movable scroll and a front surface of the middle housing facing and supporting the same; a passage for introducing high-pressure fluid into the ring-shaped groove; and at least one ring-shaped seal ring fit movably in the ring-shaped groove.
In the scroll compressor of the present invention, at least one backpressure chamber is formed in either of a back surface of an end plate of a movable scroll and a front surface of a middle housing facing the same and a high-pressure fluid compressed in a working chamber is introduced into the backpressure chamber in order to pressurize the backpressure chamber, so a thrust load acting on a sliding contact surface supporting the movable scroll in an axial direction by the middle housing becomes smaller. Even when the working pressure becomes extremely high due to use by the compressor for compressing a supercritical pressure fluid etc., the thrust load supporting surface of the movable scroll becomes a fluid lubrication state, so the coefficient of friction becomes small and the mechanical loss is reduced.
In the scroll compressor of the present invention, leakage of the high-pressure fluid introduced into the backpressure chamber to the suction chamber or other low-pressure side is prevented by fitting at least one seal ring in the backpressure chamber. One of the characterizing features of the present invention is that this seal ring can move in the backpressure chamber. Therefore, if a high-pressure fluid is supplied into the backpressure chamber, this pressure causes the seal ring to move in the backpressure chamber and be pressed against the other surface, whereby the contact pressure required for sealing is generated.
In the present invention, as one mode of movement of the seal ring, the seal ring can incline (move) slightly in sectional shape due to being pressed by the high-pressure fluid in the backpressure chamber and thereby form a narrow width ring-shaped contact region where the backpressure becomes higher with the other surface it contacts. A high sealing action is obtained by the higher contact pressure, narrow width, ring-shaped contact region, so leakage of the high-pressure fluid from the backpressure chamber is prevented. The seal ring is biased by the high-pressure fluid introduced into the backpressure chamber, but to further additionally bias the seal ring, it is possible to provide an elastic member behind the seal ring.
In the scroll compressor of the present invention, it is possible to provide two seal rings in one backpressure chamber. In this case, a first seal ring is fit along an outer circumference of a ring-shaped groove forming the backpressure chamber, while a second seal ring is fit along an inner circumference of the ring-shaped groove. These seal rings can be fabricated from materials such as rubber, plastic, or metal having wear resistance and oil resistance and elasticity. The first seal ring can be made one having a portion facing the portion of the outer circumference of the ring-shaped groove close to the bottom of the groove which forms a ring-shaped projection of a larger outer diameter than the diameter of the outer circumference of the ring-shaped groove in the no-load state before being fit in the backpressure chamber, while the second seal ring can be made one having a portion facing the portion of the inner circumference of the ring-shaped groove close to the bottom of the groove which forms a ring-shaped projection of a smaller inner diameter than the diameter of the inner circumference of the ring-shaped groove in the no-load state before being fit in the backpressure chamber. Due to this, the sectional shapes of the first and second seal rings incline (move) more easily in the backpressure chamber.
To form the ring-shaped projections at the seal rings, it is possible to form tapered surfaces at least at part of the outer circumference of the first seal ring and the inner circumference of the second seal ring. Due to this, it is possible to form sharp edge projecting rims at part of the ring-shaped projections to enhance the contact pressure and the sealing action. Further, it is possible to arrange an elastic member between the first seal ring and second seal ring to bias the first seal ring toward the outer circumference of the ring-shaped groove and bias the second seal ring toward the inner circumference of the ring-shaped groove. The biasing action of the elastic member improves the sealing action of the seal ring. Note that even when the sectional shapes of the first and second seal rings in the no-load state before being fit in the backpressure chamber are made rectangular, including square, and are not formed with ring-shaped projections, the corners of the rectangular sectional shapes act as ring-shaped projections, so substantially the same effects are obtained.
In the present invention, instead of independent seal rings, it is possible to integrally form a first seal ring part to be fit along the outer circumference of the ring-shaped groove forming the backpressure chamber, a second seal ring part to be fit along the inner circumference of the ring-shaped groove, and a connecting part integrally connecting the first seal ring part and second seal ring part. This reduces the number of parts, so facilitates assembly and reduces costs. Note that when there is a connecting part, it is possible to use at least part of that connecting part as a seal ring part and bring it into direct contact with the surface of the middle housing or other member. These parts of the integrally formed seal ring may also be fabricated by a material such as rubber, plastic, or metal having wear resistance, oil resistance, and elasticity.
When there is a connecting part, it is possible to form at least one communicating hole in the connecting part. Due to this, the same pressure acts at the two sides of the connecting part, so even when two seal ring parts are connected by the connecting part, the two seal ring parts work in the same way as if they were independent. When the two seal ring parts are connected in this way, it is possible to arrange an elastic member between the first seal ring part and second seal ring part to bias the first seal ring part toward the outer circumference of the ring-shaped groove and bias the second seal ring part toward the inner circumference of the ring-shaped groove.
In the scroll compressor of the present invention, it is possible to provide a seal ring in the backpressure chamber and enable it to move toward the surface of the other member and to provide an elastic ring-shaped seal member such as an O-ring between its side surface and the side surface of the ring-shaped groove (backpressure chamber) facing it to complementarily seal that portion.
The seal ring in this case may be made one having a superior self-lubricating action and high hardness by selecting one comprised mainly of for example carbon, metal, plastic, or ceramic. While this enables the wear resistance at the surface in sliding contact with the other member to be enhanced, the sealing action between the seal ring and the wall surface of the ring-shaped groove (backpressure chamber) receiving it may fall, but the O-ring or other ring-shaped sealing member supplements the sealing action at that portion, so a high sealing action is obtained as a whole.
The O-ring or other ring-shaped seal member can be stably supported at a predetermined position of one of the seal ring or wall surface of the backpressure chamber (ring-shaped groove) facing the same by forming a support part such as a ring-shaped groove or cutout part at that position.
In the scroll compressor of the present invention, it is possible to form a flange increasing the sliding area with the opposing surface at the ring-shaped seal ring sealing the backpressure chamber. This increases the seal area and enables a reduction of the contact pressure, so can reduce the wear due to the sliding friction. Further, since the seal ring presses against the other surface, it is possible to cause the high-pressure fluid to reliably act on a predetermined surface of the seal ring.
Even when using a seal ring having a superior self-lubricating action and high hardness which is resistant to deformation, it is possible to form the seal ring by a first seal ring part to be fit along the outer circumference of the ring-shaped groove forming the backpressure chamber, a second seal ring part to be fit along the inner circumference of the ring-shaped groove, and a connecting part integrally connecting the first seal ring part and second seal ring part. This reduces the number of parts and facilitates assembly. In this case as well, it is possible to form communicating holes in the connecting part connecting the two seal ring parts to cause the two seal ring parts to function in the same way as two independent seal rings.
The scroll compressor of the present invention may be configured as a xe2x80x9cmotorized typexe2x80x9d where a motor directly attached to the housing directly drives the rotation of its shaft or may be configured so that an external prime mover such as an internal combustion engine mounted in a vehicle drives the rotation of its shaft. One of the preferred applications for the scroll compressor of the present invention is that of a refrigeration compressor where the fluid to be compressed is a refrigerant flowing through a refrigeration cycle, in particular one set so that the pressure of the refrigerant after being compressed becomes a level of at least the critical pressure of the refrigerant.